An Improved Elastoplastic Constitutive Model for Stratum Subsidence Analysis of Gas Hydrate-Bearing Sediments

It is very important for the safe and efficient exploitation of natural gas hydrates to accurately characterize the mechanical properties of gas hydrate-bearing sediments (GHBSs). However, current research faces several significant challenges, particularly in the constitutive modeling of GHBS and its numerical implementation. Based on the modified Cam–Clay model, this paper develops an elastoplastic constitutive model of GHBS (GHBS-MCC model). To characterize the compression behavior of GHBS, a hydrate-saturation-dependent crushing stress parameter was introduced to quantify the particle breakage effects. The model’s accuracy was systematically validated through a series of triaxial shear and isotropic compression tests. The results demonstrate that the GHBS-MCC model can accurately predict the stress–strain curves of GHBS under varying hydrate saturation and confining pressure conditions. Moreover, the model reliably simulates the compression behavior across different loading scenarios. Compared with the MCC model, the GHBS-MCC model provides a more accurate characterization of the mechanical behavior of GHBS. A numerical application of the GHBS-MCC model was developed using an implicit integration algorithm. The program was applied to investigate stratum subsidence issues induced by gas hydrate extraction. During gas hydrate dissociation, stratum subsidence progressively extends from the hydrate-bearing layer to both the overlying and underlying layers. The impact is more pronounced in the overlying layer. In practical engineering applications, special monitoring emphasis should be placed on the stratum behaviors of both the hydrate layer and its overburden. The findings can present theoretical support for the assessment of reservoir safety in actual hydrate exploitation.